Anthropic API / Anthropic API

Anthropic SDK Mid-stream SSE Overloaded Error Returns Wrong Status Code (200 vs 529)

Developer using anthropic SDK streaming sees overloaded_error arrive as HTTP 200 SSE event; SDK creates bare APIStatusError(200) instead of OverloadedError(529); fallback/retry logic breaks because status check >= 500 never matches Includes evidence for Anthropic API troubleshooting demand.

Source-backed Last updated May 17, 2026 1 source Needs local verification

Category: Anthropic API
Error signature: Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic
Quick fix: Reduce request pressure, check quota or plan limits, and retry with backoff instead of immediate repeated requests.
Updated: May 17, 2026
Verification status: Source-backed
Evidence: 1 public source URL

Before you change production

This page includes public source URLs in the imported troubleshooting record. Compare those references with your version and environment before applying changes.

Reproduce the smallest failing action and save non-secret logs before changing configuration.
Check versions for Anthropic API, related SDKs, package managers, CI runners, and hosting providers.
Change one setting or dependency at a time, then rerun the same failing command or request.
Avoid destructive commands, credential rotation, billing changes, or security relaxations without a rollback plan.

What this error means

Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic is a Anthropic API failure pattern reported for developers trying to developer using anthropic sdk streaming sees overloaded_error arrive as http 200 sse event; sdk creates bare apistatuserror(200) instead of overloadederror(529); fallback/retry logic breaks because status check >= 500 never matches. Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issue anthropics/anthropic-sdk-python#1258 (closed 2026-03-31). Very specific technical bug: _streaming.py passes original HTTP 200 response to _make_status_error, so overloaded_error type is ignored. Impacts production retry logic (e.g., pydantic-ai FallbackModel). High commercial value: misdiagnosed server errors cause wasted API calls on paid accounts. Category: Anthropic API (exact match). Not covered.

Common causes

GitHub issue anthropics/anthropic-sdk-python#1258 (closed 2026-03-31). Very specific technical bug: _streaming.py passes original HTTP 200 response to _make_status_error, so overloaded_error type is ignored. Impacts production retry logic (e.g., pydantic-ai FallbackModel). High commercial value: misdiagnosed server errors cause wasted API calls on paid accounts. Category: Anthropic API (exact match). Not covered.

Quick fixes

Confirm the exact error signature matches Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic.
Check the Anthropic API account, local tool state, and provider configuration involved in the failing workflow.
Reduce request pressure, check quota or plan limits, and retry with backoff instead of immediate repeated requests.

Platform/tool-specific checks

Verify the command, editor, extension, or API client that produced the error.
Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

Capture the exact error message and the command, editor action, or request that triggered it.
Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
Review the source evidence below and compare it with your environment.
Apply one change at a time and rerun the smallest failing action.
Keep the working fix documented for the team or deployment environment.

How to prevent it

Keep provider/tool configuration documented.
Record non-secret diagnostics such as tool version, provider name, model name, and command path.
Add a lightweight check before CI or production workflows depend on the tool.

Diagnostic flow for this page

Match Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic exactly before applying the quick fix.
Compare the failing environment with Anthropic API versions, account scope, provider settings, and deployment context.
Check the listed common causes in order, starting with the cause that best matches your logs.
Use the evidence status below to decide whether to confirm against public sources or official documentation.
Apply one reversible change, rerun the smallest failing action, and keep rollback notes.

FAQ

What does Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic mean in Anthropic API?

Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic indicates the workflow described by "Anthropic SDK Mid-stream SSE Overloaded Error Returns Wrong Status Code (200 vs 529)" failed in a Anthropic API context. Start by confirming the exact signature and the component that emitted it.

What should I check first for Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic?

Check whether this cause matches your environment: GitHub issue anthropics/anthropic-sdk-python#1258 (closed 2026-03-31). Very specific technical bug: _streaming.py passes original HTTP 200 response to _make_status_error, so overloaded_error type is ignored. Impacts production retry logic (e.g., pydantic-ai FallbackModel). High commercial value: misdiagnosed server errors cause wasted API calls on paid accounts. Category: Anthropic API (exact match). Not covered.

Is the Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic guidance source-backed?

The "Anthropic SDK Mid-stream SSE Overloaded Error Returns Wrong Status Code (200 vs 529)" page is labeled source-backed. It has 1 public source URL from github.com, so use that evidence status when deciding how much additional verification you need.

When should I avoid the quick fix for Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic?

For "Anthropic SDK Mid-stream SSE Overloaded Error Returns Wrong Status Code (200 vs 529)", avoid applying "Reduce request pressure, check quota or plan limits, and retry with backoff instead of immediate repeated requests." when the error text differs, the affected version or provider is different, or the change would touch credentials, billing, DNS, production deploy settings, or irreversible data.

What should I collect before debugging Mid-stream SSE overloaded_error returns status_code=200 instead of 529 — fails fallback retry logic?

For "Anthropic SDK Mid-stream SSE Overloaded Error Returns Wrong Status Code (200 vs 529)", collect the failing Anthropic API command or request, non-secret configuration, versions, timestamps, request IDs when available, and the smallest reproduction that still triggers the signature.